Keep Learning

As of 2016, APCO International has the largest U.S. membership base of any public safety organization and serves public safety communications personnel throughout the world, according to the organization. Created in 1929, the California Highway Patrol is responsible for ensuring enforcement of uniform traffic laws for safe travel on the state's highway system, according to the Patrol. The Dallas Police Department dispatches signal codes 15, 19, 35 and 44 as Code 3 communication code calls automatically, which means the responder uses emergency lights and sirens, explains the Federal Highway Administration.

Between the 1920s and 1930s, police began using ten-codes for radio communications to keep traffic short, according to About.com. An Illinois State Police communications director, Charles Hopper, established the first code set. To make sure officers could hear the entire radio message, their instructors taught them to pause for a moment between turning the microphone on and talking, and to say the number 10 before saying the numeric code.